The present invention relates to a projector for enlargedly projecting an optical image on a screen.
As a device for displaying a large image, there has been known a projector which generates an optical image in accordance a video signal by illumination light and enlargedly projecting the optical image of illumination light on a screen by means of a projection lens.
A conventional projector is described with reference to a construction diagram of FIG. 11. Light emitted from an illuminator 51 is split into wavelength regions of three colors of red (R), green (G) and blue (B) by dichroic mirrors 52 and 53. Specifically, beams of light within a wavelength region of R reflected by the dichroic mirror 52 are reflected by a full-reflection mirror 54, and illuminate an image panel 56 after passing a field lens 55. Beams of light within wavelength regions of G and B pass the dichroic mirror 52. Thereafter, the beams of light within the wavelength region of G are reflected by the dichroic mirror 53, and illuminate an image panel 58 after passing a field lens 57, whereas the beams of light within the wavelength region of B pass the dichroic mirror 53, pass a field lens 63 after being introduced thereto by a relay optical system constructed by two full-reflection mirrors 61, 62, and illuminate an image panel 64.
Optical images formed respectively by the three image panels 56, 58, 64 are combined by a dichroic prism 65. Specifically, the optical image of R formed by the image panel 56 is propagated straight into the dichroic prism 65 as incident light, is reflected at 90.degree. by a first dichroic mirror portion 65a after having been incident thereon at 45.degree., and emerges toward a projection lens 66. The optical image of B formed by the image panel 64 also is propagated straight into the dichroic prism 65 as incident light, is reflected at 90.degree. by a second dichroic mirror portion 65b after having been incident thereon at 45.degree., and emerges toward the projection lens 66. The optical image of G formed by the image panel 58 is all propagated straight through the dichroic prism 65 as incident light, without being reflected by the first and second dichroic mirror portions 65a, 65b, and emerges toward the projection lens 66. The optical images thus formed on the three image panels 56, 58, 64 are combined by being directed toward the projection lens 66 located in the same direction while the axes of polarization thereof is made to correspond with the optic axis. The combined optical image is enlargedly projected on the screen via the projection lens 66.
However, the conventional projector is influenced by the aberration of the lenses used in the relay optical system and the like. Accordingly, the illumination area for projecting the optical image on the image panel 64 is required to be set large. An ideal illumination area in the absence of aberration and an actual illumination area in the presence of aberration are shown in FIGS. 12A and 12B, respectively. In FIGS. 12A and 12B, an area enclosed by broken line is an illumination area and a rectangular area enclosed by solid line is a display surface of the image panel 64. When the aberration of the lens 60 and the field lens 63 is large, the illumination area on the image panel 64 is not similar in shape to the display surface of the image panel 64, and its four corners are rounded.
The illumination area is set larger than the display surface 64 in view of the displacement of the lenses and mirrors. However, the larger the illumination area, the greater a light loss becomes. In this state, the large aberration of the lens 60 and the field lens 63 means that the four rounded corners are larger. This stands for a smaller degree of tolerance for the displacement. In order to ensure a targeted tolerance in this state, the illumination area needs to be further enlarged. However, the light loss becomes even larger accordingly.
Further, the lens 60 and the field lens 63 are coated with three layers of lens coatings to improve light transmission.